Protein import into complex plastids

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Many algae evolved in secondary endosymbiosis. Here a unicellular, eukaryotic cell harboring a plastid surrounded by two membranes was internalized by another eukaryote. In the course of the co-evolution of this cell-within-a-cell the phototrophic cell was reduced to a complex plastid surrounded by either three or four membranes. From many genome projects it is known that the genomes of complex plastids have not the capacity to encode all plastid-located proteins. Thus, for the symbiontic interaction a transport system was established to guarantee transport of nucleus-encoded plastid protein across the plastid surrounding membranes. In case of the plastids of diatoms, which are surrounded by four membranes, we have identified for the first time the translocators of the second outermost and, in a cooperation project, of the third membrane. Additionally we have shown that these translocators are present in many other algae as well as in some intracellular parasites. In the project applied here, we will focus on the translocator complex in the second outermost membrane in respect to interacting factors and its structure. For that we will apply strategies firstly used in a secondarily evolved model organism. In addition it is planned to determine the protein structure of important translocator complex components. We expect from our work in-depth insights into the translocator complex and its functions. As this complex is in respect to its membrane components homologous to the ERAD machinery of eukaryotic cells, we expect that the community working on ERAD will profit from our work as well.